I see something odd when I upgraded from 7.5.3 to 7.5.4.1.
I closed the board performed the upgrade.
After it was complete it prompted me to open the board. It did not work. In fact I got a blank page when I selected submit.
Going to control panel >>Home did not open the board, still a blank page after submitting.
The only way to open the board was to goto Control Panel » Primary Settings and deselect "Close Board?"
I checked the permission settings in the control panel and all show okay.

Update, if I try to close the board again after updating using the link in control panel>>home it does not close the board I just get a blank page.
To open and close the board I must goto Control Panel » Primary Settings and select/deselect "Close Board?"

Hmm, blank pages are always tough to figure out since it should at least give some type of error. Unless your php is configured to only log the errors. You might check your webserver error logs if so, to see if there is anything in there.

Okay I found the problem.
dotoggleopen.php was at 0 bytes. I re uploaded it and it is working now from the home page of the control panel.

So put that up to a ftp program error I guess.
Not a Bug!!!